FAQ on principles of fluid and flow dynamics of Blood

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Name two factors that determine blood flow to an organ:

These two factors are blood pressure and resistance.

What factors determine resistance to blood flow? Explain how each affects resistance:

Size of lumen: The more the size, the less the resistance.

Blood viscosity: The less the viscosity, the lower the resistance. Total vessel length: The more the length, the more the resistance.

What is the relationship between blood vessel diameter and resistance to blood flow? What is the significance of this?

The more the blood vessel diameter, the lower the resistance. Blood vessels that have plaque deposited on their walls offer higher resistance leading to heart disease. Diameter is varied to control vasoconstriction and vasodilatation.

What determines blood viscosity?

Viscosity is determined by ratio of RBCs to plasma volume.

What factors are responsible for laminar (streamline) flow becoming turbulent?

Turbulence occurs when laminar flow is disrupted by narrowed arteries or heart valves. It also happens during exercise.

What are the differences in the pressures in the capacitance and the resistance vessels? What is a capacitance vessel? What is a resistance vessel?

Pressure in capacitance vessel (veins) is lower and pressure in resistance vessel (arteries) is higher.

By definition, “capacitance” vessels (mostly venules and veins) are those that can expand with blood flow – like a balloon. These vessels accommodate more blood volume in them whilst maintaining low blood pressure. These vessels are more flexible.

"Resistance" vessels are those that don’t have as much elasticity and don’t expand much but keep their volume constant whiles withstanding higher blood pressures. These vessels are mostly arteries.

Many drugs work by vasodilating or vasoconstricting blood vessels. If you are given a drug that reduces the calibre of your blood vessels by 50% (1/2), what effect will this have on blood vessel resistance and blood flow?

If the caliber (diameter) is reduced by one half, resistance, according to the Poiseuille-Hagen formula, will increase 16 times and blood flow will be slowed considerably.

Why does blood flow faster in arteries and veins than in capillaries?

Because capillaries have the smallest diameter and higher resistance.

In which blood vessel is the flow of blood fastest?


Describe what is meant by the circulation time? What is the circulation time at rest?

It is the time required by the blood to flow from the right atrium back to the right atrium. It takes about one minute.

Additional Reading:

Basic Pathology

1. Cell Injury
2. Inflammation and Repair
3. Immunopathology
4. Water, Electrolyte, Acid-Base, Hemodynamic Disorders
5. Genetic and Developmental Disorders
6. Environmental Pathology
7. Nutritional Disorders
8. Neoplasia
9. Vascular Disorders
10. Heart Disorders
11. Red Blood Cell Disorders
12. White Blood Cell Disorders
13. Lymphoid Tissue Disorders
14. Hemostasis Disorders
15. Blood Banking and Transfusion Disorders
16. Upper and Lower Respiratory Disorders
17. Gastrointestinal Disorders
18. Hepatobiliary and Pancreatic Disorders
19. Kidney Disorders
20. Lower Urinary Tract and Male Reproductive Disorders
21. Female Reproductive and Breast Disorders
22. Endocrine Disorders
23. Musculoskeletal Disorders
24. Skin Disorders
25. Nervous System Disorders
26. Notes on Tissue Regeneration
27. A Table of Bleeding Disorders
28. FAQ on Structure and Function of Red Blood Cells
29. FAQ on Components of Blood
30. Notes on Hemostatic Mechanisms
31. What is Fever?
32. What is Edema?
33. FAQ on Blood Pressure
34. FAQ on principles of fluid and flow dynamics of Blood
35. Causes of Thrombocytopenia
36. Squamous cell carcinoma of head and neck mucosa
37. Four tumors which never metastasize to the brain
38. What is caustic injury?
39. What causes Peripheral Edema?

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